A seat suspension of the general type to which this invention relates may find utility in a vehicle having an unsprung chassis, such as a tractor or an earth moving machine, or in a truck or truck-tractor that has firm springs for supporting heavy cargo. In general, such a suspension comprises a seat part which supports a seat occupant, a base part which is secured to a vehicle chassis, linkage connected between the seat part and the base part to confine the seat part to substantially up and down motion, and a resilient device (spring or hydropneumatic cylinder) which is also connected between the base part and the seat part to impose yielding upward bias upon the seat part that cushions its up and down motion.
Especially in the case of seats for cab-over-engine vehicles, some operators like to have the seat arranged for absorbing abrupt fore-and-aft accelerations and decelerations as well as vertical shock forces. However, other operators of the same types of vehicles dislike such fore-and-aft shock isolation, and therefore that feature should be optional and capable of being readily cut in or cut out by the seat occupant. Whether or not fore-and-aft isolation is available, the seat should provide for fore-and-aft adjustability. With fore-and-aft isolation effective, the seat should have a static or nominal position to which it has been adjusted according to the occupant's desires and from which it makes limited shock-absorbing excursions through about equal distances forwardly and rearwardly, in each case against bias that urges the seat back to the static position.
The general object of the present invention is to provide a seat suspension having a single easily manipulated control that can be moved to one position at which the seat part has fore-and-aft shock isolation, another position in which the seat part is confined against fore-and-aft motion, and a third position in which the seat part is released for fore-and-aft adjustment through a range of positions.
Another and more specific object of the invention is to provide a seat suspension having a pair of tension springs which respectively provide for forward bias and for rearward bias on the seat part when the apparatus is in its fore-and-aft shock isolation mode, and wherein one of those springs also serves to bias a latching member to a locked position in which it releaseably holds the seat part in a desired position of fore-and-aft adjustment, while the other of said springs provides for toggle action of a control member whereby fore-and-aft isolation is either cut in or cut out, to hold that control member in whichever position is selected for it.
It is also an object of this invention to provide a simple control mechanism for a seat suspension wherein a seat part is mounted on a suspension part for fore-and-aft motion relative thereto, said control mechanism comprising a latching member that is movable to and from a normal position wherein it has locking engagement with the suspension part and a control member that has three defined positions, namely, a first position wherein the control member holds the latching member out of its normal position to permit fore-and-aft adjustment of the seat part, a second position wherein the control member maintains the seat part locked to the latching member and allows the latter to remain in its normal position so that the seat part is confined against fore-and-aft motion, and a third position in which the latching member likewise remains in its normal position but the seat part is allowed to make limited forward and rearward shock isolating excursions relative to it.
In general, these objects of the invention are achieved in structure wherein a seat part is supported on a suspension part for fore-and-aft motion relative thereto, which structure comprises a latching member and cooperating means on the seat part and on the latching member whereby the latter is connected with the seat part to swing relative thereto about a first axis. Such swinging carries the latching member between a normal position, wherein a latch part on the latching member engages said suspension part to confine the latching member against fore-and-aft movement relative to the suspension part, and a releasing position wherein the latch part is disengaged from the suspension part. Said cooperating means further provides for limited fore-and-aft sliding of the seat part relative to the latching member when the latter is in its normal position. There is also a manually shiftable control member, and pivot means connecting said control member with the latching member for swinging relative thereto about a second axis which is spaced from and parallel to said first axis. Such swinging in one direction carries the control member from an intermediate position to a first limit position wherein the control member leaves the latching member free for fore-and-aft sliding relative to the seat part. Cooperating abutment means on the seat part and on the control member are engaged when the control member is in said intermediate position, to confine the control member against fore-and-aft movement relative to the seat part, thus locking the seat part to the latching member; and said abutment means provided a fulcrum about which the control member can be swung in the opposite direction, from its intermediate position to a second limit position, while said pivot means constrains the latching member to swing to its releasing position.
With the control member in its intermediate position, one tension spring, connected between the latching member and the seat part, yieldingly resists rearward motion of the seat part and another tension spring, connected between the control member and the seat part, yielding resists forward motion of the seat part. Said one tension spring also serves to bias the latching member to its latching position; and said other tension spring also imposes a toggling bias force upon the control member as it is swung between its intermediate position and its first limit position.